1. Field of the Invention
The present invention relates generally to imaging systems and methods. More particularly, the present invention is directed to x-ray imaging systems and methods that determine acquisition parameters such as frame rates and/or pulse lengths as a function of detected motion.
2. Background Discussion
Radiography is the use of certain spectra of electromagnetic radiation, usually x-rays, to image a human body. Angiography, a particular radiographic method, is the study of blood vessels using x-rays. An angiogram uses a radiopaque substance, or contrast medium, to make the blood vessels visible under x-ray. Angiography is used to detect abnormalities, including narrowing (stenosis) or blockages (occlusions), in the blood vessels throughout the circulatory system and in certain organs.
Cardiac angiography, also known as coronary angiography, is a type of angiographic procedure in which the contrast medium is injected into one of the arteries of the heart, in order to view blood flow through the heart, and to detect obstruction in the coronary arteries, which can lead to a heart attack.
Peripheral angiography, in contrast, is an examination of the peripheral arteries in the body; that is, arteries other than the coronary arteries. The peripheral arteries typically supply blood to the brain, the kidneys, and the legs. Peripheral angiograms are most often performed in order to examine the arteries which supply blood to the head and neck, or the abdomen and legs.
Conventional x-ray imaging systems that are used in radiography and angiography for diagnostic or interventional procedures utilize fixed frame rates. That is, a particular number of images are acquired per second. The fixed frame rate is usually selected based on the particular procedure being performed.
Some examples of procedures using conventional x-ray imaging systems that utilize fixed frame rates include:                obtaining a single image for radiographic applications (for example, a chest x-ray);        obtaining a sequence of fluoroscopic images (a fluoroscopic scene), running at 10 fps (frames per second), to place a catheter in a neurological procedure;        obtaining a sequence of acquisition images (an acquisition scene), running at 30 fps, to visualize the left coronal arteries of an adult in a coronary application;        obtaining an acquisition scene, running at 60 fps, in a pediatric application;        a fluoroscopic scene, running at 30 fps, to place a catheter, and to thereby obtain the coronary acquisition sequence described above; and        a three-dimensional run (for example, a sequence of images while an x-ray tube and detector rotate around an object), running at 30 fps.        
One drawback of conventional x-ray imaging systems is that while they permit selection between different frame rates based on procedure and application, unfortunately they do not permit frame rates to be changed during a scene. (A scene is defined as a consecutive sequence of images which is acquired while an operator operates the x-ray release switch without interruption; for example, a footswitch or a hand switch.) In order to change the frame rate, the operator must stop the sequence, change the frame rate via a user interface, and resume the procedure, which subsequently generates a new image sequence with the new frame rate setting.
Another drawback to conventional x-ray imaging systems is that an operator is limited to the selection of a small finite number of possible frame rates. For example, present x-imaging ray systems only support frame rates of 60, 30, 15, 8, 4, 2, 1, and 0.5 frames per second. Other frame rates in between are not supported. When object motion is present, information may be lost if the operator has not, for whatever reason, increased the frame rate. Conversely, when object motion is not present, if the operator has not, for whatever reason, decreased the frame rate, both the patient and the operator will be exposed to a greater than necessary dose of x-rays.
Still a further drawback to conventional x-ray imaging systems is that a pulse length (that is, a length of the x-ray pulse used to acquire an image) cannot be adjusted automatically as a function of object motion. The pulse length is an important factor in obtaining optimum image quality—pulse length determines sharpness within a single image. When object motion is present, the acquired object in the image may appear less sharp, or more smeared, the longer the pulse length of the x-ray pulse. Therefore, a minimum pulse length is optimal. However, other parameters may limit a short pulse length, for example, the tube power limitations.
In general, a drawback of conventional x-ray imaging systems is the use of fixed and predetermined image acquisition parameters, that can only be changed, or modified, by an operator by stopping and then resuming an imaging sequence.
Therefore, it would be an advancement in the state of the imaging art to provide a variable frame rate x-ray imaging system that enhances image quality and improves the efficiency of the imaging procedure.
It would be an additional advancement in the state of the art to provide a variable pulse length x-ray imaging system that enhances image quality.
It would be further advantageous to provide an x-ray imaging system that supports both a variable frame rate and a variable pulse length, so as to maximize the image quality and the efficiency of the imaging procedure.
In general, it would be an advancement in the imaging art to provide an imaging system that dynamically adjusts image acquisition parameters as a function of detected motion.